The present invention relates generally to reception and processing of spread spectrum signals. More particularly the invention relates to a spread spectrum signal receiver according to the preamble of claim 1 and a method of operating a spread spectrum signal receiver according to claim 13. The invention also relates to a computer program according to claim 24 and a computer readable medium according to claim 25.
Spread spectrum transmission solutions are becoming increasingly important, for instance in global navigation satellite systems (GNSS). Presently, the Global Positioning System (GPS; U.S. Government) is the dominating standard, however alternative standards exist and are expected to gain increased importance in the future. So far, the Galileo system (the European programme for global navigation services), the Quasi-Zenith Satellite System (QZSS; Advanced Space Business Corporation in Japan) and the Global Orbiting Navigation Satellite System (GLONASS; Russian Federation Ministry of Defense) constitute the alternative standards. Due to different signal formats and frequency bands of these standards a navigation receiver adapted for one GNSS, say GPS, is not able to receive and process signals from a satellite that belongs to a different GNSS, say the Galileo system.
A multi-mode receiver is required to enable use of signals from the satellites of different systems. However, including multiple receiver chains in a single device is not only expensive, it also renders the device bulky and heavy, particularly if more than two signal formats are to be processed.
Instead, to this aim, a programmable software receiver solution is desired. Namely, in such a design, the signal processing principles may be altered according to which signals that presently shall be received and processed. A software-based receiver is also desirable in cases where the GNSS receiver is co-existing with other types of signal receivers, signal processing devices and/or software applications, for example in a laptop computer, a mobile telephone or a PDA (Personal Digital Assistant).
Today, relatively few software-based solutions exist that implement GNSS receivers. The vast majority of GNSS receivers on the market include signal processing hardware, which is optimized, and exclusively used, for processing satellite signals and deriving data (e.g. reflecting position, time, distance, velocity or altitude). A number of hardware solutions for processing GPS signals, which utilize the receiver's power resources in a comparatively efficient manner are also known.
For example, the patent document U.S. Pat. No. 5,592,173 describes a GPS receiver having a normal mode and a low power standby mode. In the standby mode, the operating power is inhibited in the antenna and the frequency downconverter. Moreover, in this mode the system clock is inhibited in the digital processing system, and the microprocessor clock is inhibited in the microprocessor system. By alternating between operation in the normal mode and the standby mode the average power consumption can be reduced in relation to a permanent normal-power mode operation.
This possibility of alternately switching the receiver on and off is advantageous because it economizes the receiver's power resources, and thus allows a relatively long battery life. However, for hardware designs of this type the flexibility is limited.